Print-setting apparatus

ABSTRACT

Print-setting apparatus of the kind which employs a number of separately drivable character-bearing belts in side-by-side relation is provided with electrically operated stepping means for positioning the various belts in desired locations. Slotted code wheels having precise driving and structural relationships with the driving system for the belt-positioning apparatus are employed for counting the incremental movements of that apparatus. Results of the counting are used for monitoring and controlling the functioning of the print-setting apparatus as a whole.

United States Patent [1 1 Hubbard et al.

[ 1 Aug. 7, 1973 PRINT-SETTING APPARATUS Inventors: David W. Hubbard, Stamford; Alton B. Eckert, Jr., Norwalk, both of Conn.

[52] U.S. Cl. 101/93 C, lOl/l 11 [51] Int. Cl 1 B4lj 1/20 [58] Field of Search 101/93 C, -97, 101/99, 110, 111; 235/61 [56] References Cited UNITED STATES PATENTS 3,640,216 2/1972 Piazza 101/93 C 2,906,200 9/1959 Pfleger 101/93 C 3,682,282 8/1972 Carboni et al 101/111 X 3,490,365 l/l970 Roche 101/93 C 3,120,801 2/1964 Davies et al. 101/93 C 3,572,239 3/1971 Grenier 101/99 2,686,468 8/1954 Bliss 101/99 X 3,468,479 9/1969 Sauter l0l/99 X Primary Examiner-Robert E. Pulfrey Assistant Examiner-L. M. Coven Attorney-William D. Soltow, Jr., Albert W. Scribner et a1.

57 ABSTRACT Print-setting apparatus of the kind which employs a number of separately drivable character-bearing belts in side-by-side relation is provided with electrically operated stepping means for positioning the various belts in desired locations. Slotted code wheels having precise driving and structural relationships with the driving sys tem for the belt-positioning apparatus are employed for counting the incremental movements of that apparatus. Results of the counting are used for monitoring and controlling the functioning of the print-setting apparatus as a whole.

3 Claims, 8 Drawing Figures CARD READER T El PATENTED AUG 7 I973 SHEET 1 OF 3 PATENTED AUG 7 I973 SHEET 3 [IF 3 FIG.7

FIG.7(1.

PRINT-SETTING APPARATUS BACKGROUND OF THE INVENTION This invention relates to automatic print-setting apparatus and particularly to compact, office-usable apparatus which is suitable for the job-lot printing of retail price tickets or the like.

Printers have a plurality of side-by-side print wheels or belts for printing alphanumeric or other symbols onto sheet or strip material are well known. In particular, such devices have been used in the printing of retail price tickets for a variety of merchandise. In such printers there may be a number of character-bearing belts positioned side-by-side and each serving for the selective location of printable characters at a printing station. Such printing devices generally have readout windows for ascertaining the characters positioned for printing and have some means for moving each character-bearing belt until the symbols appearing at the readout windows indicate that printing characters have been arrayed in the order desired for printing.

The positioning of the print characters on such a printing device has commonly been performed by hand operation wherein each print belt drive wheel must be engaged by a hand-operated device and rotated to position the proper print character for each of the number of belts of the printing device. Typically a retail sales ticket may have a pair of print heads having to belts, with one print head being adjacent the other for printing alphanumeric characters in one row and a marking code such as a bar code in the other. It is readily apparent that moving each of the belts manually to position the appropriate print character at the print head is a time-consuming and expensive operation.

Accordingly, it is an object of the present invention to provide highly reliable print-selling apparatus for automatically positioning print characters in a printing system of the kind described above.

It is a further object of the invention to provide printsetting apparatus of the above kind wherein the characters to be set on the printing device can be set automatically from information on a punched card or like information storage means.

It is a still further and more particular object of the invention to provide in apparatus of the kind specified extremely precise and fail-safe means for guarding against error in the selection and placement by the print-setting mechanism of the characters to be imprinted on the print-receiving surface.

Other objects of the invention will in part be obvious and will in part appear hereinafter.

The invention accordingly comprises the features of construction. combinations of elements, and arrange ment of parts which will be exemplified in the constructions hereinafter set forth, and the scope of the invention will be indicated in the claims.

For a fuller understanding of the nature and objects ofthe invention, reference should be had to the following detailed description taken in connection with the accompanying drawings, in which:

FIG. 1 is a schematic view in perspective of the automatic print setting apparatus of the invention.

FIG. 2 is an elevation view of a sensing and signal generating device used in the practice of the invention.

FIG. 3 is a partial sectional view taken on line 33 of FIG. 2.

FIG. 4 is a somewhat enlarged side view of a segment of one of the elements of FIG. 2.

FIG. 5 is a greatly enlarged view of one of the elements of FIG. 4.

FIG. 6 is an enlarged partially schematic view of a single component of one of the elements of FIG. I, and

FIGS. 7 and 7a are enlarged fragmentary views of certain of the elements of FIG. 1, these elements being shown in two different operating positions.

SUMMARY OF THE INVENTION The invention relates to automatic print-setting apparatus having drive members selectively engageable with a number of character-bearing structures. These structures may, for example, comprise wheels, belts or the like supporting a series of printable alphanumeric symbols and adapted to be driven by the drive members when engaged by them. The several character-bearing structures are in side-by-side position or otherwise closely associated, and each drive member is movable in incremental steps under precise automatic control to successively engage predetermined ones of the aforementioned structures and to drive these structures in a character-positioning mode. Once the positioning function has been performed for a first structure, the drive member is then moved a preselected distance to engage the next eligible structure and to drive it in similar fashion to the first. This process is repeated automatically until all of the preselected characters for the printing mechanism are set.

The drive member is moved in both its characterpositioning and engagement-seeking modes by stepping motors which require a predetermined number of energizing pulses to move the member from one significant position to another. The number of discrete motive steps required to produce significant motion is such that great precision of placement can be attained. Monitoring of the motion of the driving member is accomplished with high reliability by a precision motiondetecting and communicating mechanism, which in a particular embodiment of the invention comprises a code wheel and cooperating photocell sensors, the turning of the code wheel being synchronously related to the motion of the driving system. by means of pulses produced in the sensors by passage of elements of the code wheel, a combined memory an logic system keeps track of the code wheel position and accordingly monitors the positions of the various driving mechanisms, thus controlling, in the final analysis, the positioning of the various printable characters in accordance with instructions given in advance to the memory and logic system. By interaction of the sensors with the memory and logic system, motion of the various driving mechanisms is terminated when all of the preselected printing characters have been driven to their respective printproducing stations.

Predesigned input information may be introduced into the controlling logic system by conventional input means, such as a card reader, wherein the coded card is provided with all of the information needed to set the selected print characters in their proper positions for a given print-out. Thus, as the card reader scans the information card, each printing character will be automatically and very accurately positioned in its predetermined proper location by operation of the various stepping motors coacting with the several sensing devices and the associated memory and logic system.

Further features of the invention provide means for sensing the home position for each set of printing characters, means utilizing limited back-step motion of the driving systems for facilitating meshing of driving members with the driven parts of the successive cha raeter-bearing structures, and superimposed back-up monitoring means for confirming that the actual position of the parts conforms exactly to that tentatively signalled by the code wheels and sensing devices operating in their primary mode.

DETAILED DESCRIPTION OF THE INVENTION The Print-Positioning Assemblies and Their Drive Mechanisms In FIG. I two similar and generally coordinated printpositioning assemblies are shown at 10 and 1], respectively. For assembly there is a printing station at location 12 and for assembly 11 a similar printing station at location I3. A table or platen 14 underlies these printing stations, and a continuous sheet of imprintable material I6 lies between the table and the printpositioning assemblies at the printing stations. It will be understood that this sheet may be moved continuously or intermittently over the surface of the table in order that various areas of its surface may be successively imprinted.

Each of the printing assemblies and 11 includes a set of separate character-bearing structures, which, in FIG. I, are shown in independently movable belts 10a and Ila respectively. The number of such structures (for belts) in a given assembly may be as many as desired, e.g., from two to or more). Each belt is assumed to carry at appropriately spaced intervals over its external longitudinal surface printable characters chosen to meet the needs of the user. For the ticketprinting usage which is a principal focus of the present application, the belts of assembly I0 may, for example, carry conventional and directly readable alphanumeric characters while the belts of assembly 11 may carry machine-readable symbols in combination with alphanumeric symbols which correspond on a one-to-one basis to the machine readable symbols.

Each of the belts of the two assemblies has associated with it a carrying member, which, in the construction illustrated, comprises a wheel or pulley as indicated at 20 and 20a, respectively. It will be understood that there are a series of identical and aligned wheels lying behind the wheels 20 and 20a and that these correspond in number to the number of belts. As the wheels turn, say in clockwise direction, the belts are moved accordingly and the characters which they carry are transported successively to the respective printing stations.

In a specific application of the invention, printable characters are carried only on one half of the various belts, for example, on the half of the belts 10a and 11a of FIG. I which, in the starting or home" position of the belts, would lie to the left of the vertical center line of the belts 20 and 20a of FIG. 1. In this application, the other half of each belt carries man-readable alphanumeric symbols which successively appear at a viewing area (not designated) near the top of the assembly and which, in a stationary condition of the driving mechanism, serve to identify to the operator the character which at that moment is located at the printing station. When using this construction, it is desirable, in order to expedite the placement of characters at the printing stations, to have the various drive systems capable of both forward and backward motion. It is. therefore, to be assumed in the remainder of the description that the total system has this capability. In addition to the driving wheels 20 and 20a, the carrying system for the belts also includes, in the particular embodiment illustrated, square pulleys or guide members 22 and 22a, each of which is yieldingly spring pressed against the lower bight of the belt with which it is associated. The edgewise dimensions of these square members are such as to substantially match the displacement of the separate character-bearing elements of the belts 10a and Ila, so that each quarter-turn of one of the square members brings a new character into printable position beneath the member at its associated printing station. When all the characters intended to be printed have been set in place at the printing stations, printing is accomplished by moving the platen 14 into pressing engagement with the characters, this being re peated intermittently as the printable surface is moved from left to right. Ink or another print-producing substance is introduced into the printing area by conventional means not necessary to be shown.

Print-positioning mechanisms of the kind repre sented by assemblies 10 and 11 as so far described are known to the prior art and in themselves do not constitute the substance of the present invention. However, available versions of such assemblies lack the kind of automaticity of operation which is desirable for present day commercial application. The present invention provides simple yet highly reliable apparatus by which the print-setting functions of the various characterbearing assemblies can be carried out automatically upon the introduction into the control system (to be described below) of information (written, coded or otherwise) indicating the content of the material which is desired to be imprinted. The apparatus comprises and functions through drive means which is capable under automated control first, of locating and engaging selectively the drivable parts of each of the characterbearing structures (i.e., the belts 10a and Ila or their structural counterparts in other versions of the printsetting assembly) and then, again in accordance with preset instructions, driving each engaged characterbearing structure to a point at which the character desired to be imprinted by that structure is brought into place at the printing station. This is continued automatically pursuant to the given instructions until all of the various character-bearing structures have been drivingly engaged and brought to their desired printing locations. Meanwhile, by the remainder of the apparatus provided, the performance of these selecting and driving functions is monitored in such a way as substantially to ensure against discrepancy between the final result and the desired printing pattern as indicated by the input instructions.

The mechanisms by which the driving function described in the preceding paragraphs is to be carried out are shown in the central area of FIG. 1. The driving mechanisms per se are substantially duplicated in connection with assemblies 10 and 11, hence the driving elements of assembly 11 which correspond to those of assembly 10 are identically numbered except for the appendage to each number of the differentiating character a.

Referring by way of example to printing assembly 10, there is provided in connection with that assembly a rotatable drive shaft 30 having at the end nearest the print-setting assembly a driving member shown as a pinion gear 31. In the position shown, this engages a ring gear 32 constructed concentically with the circum ference of the wheel 20. It is to be understood, of course, that the wheel is supported upon a suitable bearing (not shown) so that its position in space may be maintained while it is being driven by the gear 31. In accordance with the invention, the drive shaft is also movable longitudinally with respect to the printsetting assembly 10. Accordingly, as it moves from left to right, the gear 31 can successively engage the ring gears respectively associated with the additional wheels corresponding to wheel 20 in order that each of these may be driven independently of the others. Driving movement of each wheel, of course, implies corresponding movement of the character-bearing structure carried by it.

Proceeding backward from the driven mechanisms just described toward the power source, it will be noted that the drive shaft 30 is driven in its rotary direction by the combination of a driven gear 35 and a driving gear 36 along which the driven gear is free to slide in the direction of its axis. The shaft 30 is moved in the axial direction by a carrying member 38 which is locked to the shaft in such fashion that the two necessarily move together axially, although the shaft 30 is free to rotate within the carrier 38. The carrier 38, bearing with it the shaft 30, is driven by a rack and pinion gear combination, of which the pinion is indicated by the numeral 40. It will be seen that by the combination as so far described, the driving member or gear 31 can, by appropriately controlled motion of the carrier 38, be moved into engagement with any of the succession of driving wheels 20. Moreover, by actuation of the driving gear 36 the shaft 30 can be rotated so that the driving gear 31 turns the particular wheel 20 with which it is engaged to move the character-bearing structure controlled by that wheel into whatever position is desired. In practical use, of course, the structure is driven into a position such that a particular preselected character borne by it is brought into printable position at the printing station 12.

The drive mechanism for the rotary shaft 30 comprises, in addition to the gear combination 35, 36, a motive or energizing mechanism represented schematically in FIG. 1 at M1.

This mechanism includes in the preferred embodiment of our invention a stepping motor which rotates in discrete incremental steps rather than continuously. The stepping system used to produce this result may comprise, for example, a conventional flip-flop pulsegenerating circuit (not shown) in the input to the motor element itself. Stepping motors (including energizing flip-flop circuits) useful for this purpose are well known in the art and need not be described in connection with the present invention. See, for example, pages 132 and I33 of the Mar. I9, I964 Reference Issue of the magazine Machine Design, as published by the Penton Publishing Co.

While the number chosen in arbitrary and may be varied as a matter of design, let it be assumed that the number of pulses required to produce one full revolution of the motor shaft 50 is 200. The gear ratios employed between the shaft 50 and the character-bearing belts 10a (including, of course, the relationship be tween the length ofthe belt loop and the circumference of the driving wheel of pulley 20) are designed to be such that some multiple of eight pulses (e.g. eight or 16 pulses) will produce one character step. Otherwise stated, a succession of eight stepping pulses will suffice to displace a given printing character from the printing station and to replace it by the next succeeding character. This establishment of a precise mathematical relationship between the number of stepping pulses applied and the displacement of one printing character by another is important for maintenance of the monitoring and control functions shortly to be described.

The drive shaft 30a associated with the characterbearing assembly 11 is driven by a motive system M3 operating through shaft 50a in a way which corresponds in essential particulars to the driving arrangement just described in connection with shaft 30 pertaining to character-bearing assembly 10. Axial drive motors M2 and M4 corresponding to motors M1 and M3 in respect to their ability to provide discrete incremental driving impulses are coupled respectively to shafts 52 and 52a for controlling the axial motion of the shafts 30 and 30a respectively. Moreover, in this case also, it is arranged that a precise number of driving pulses will suffice to move the driving gears 30 and 310 from a position of full engagment with a particular one of the driving sheels 20 and 21 respectively into full driving engagement with the next succeeding driving wheel in the particular character-bearing assembly involved. For example, by analogy with the rotary drive system already described it be readily possible to design the gearing arrangements at 40 and 40a respectively in such fashion that eight motive pulses applied either to the shaft 52 or the shaft 52a would move the corresponding drive gear 31 or 31a precisely from engagement with one belt drive to engagement with the next. However, other multiple-of-four drive ratios (e.g. l6 stepping pulses for each belt-to-belt transition) may be employed if desired.

INPUT CONTROL OF THE POSITIONING MECHANISMS An important aspect of the present invention consists in the provision of control and monitoring means for the driving mechanisms just described which are capable of assuring exceptionally high accuracy and reliability in the operation of the whole apparatus. It is another important aspect of the invention that these results may be obtained while directing the apparatus by use of card-punched, printed or tape-carried instructional data which is introduced at an input station.

The combination by which this is achieved may, for example, include as any instruction-entering device a card reader as indicated at 60. This will receive in know fashion a card on which has been recorded by punching or otherwise a machine-readable indication of the al phanumeric characters which are to be impressed on the print-receiving surface 16 at the station 12 and an indication of the machine-readable (and/or alphanumeric) characters which are to be impressed at station 13. These indications will be read by the card reader in an order which corresponds to the order of desired application of the various characters across the surface 16 and thus dictates the order in which these characters are to be arrayed at the respective printing stations by the character-bearing assemblies 10 and 11.

The data derived by the card reader from each card which it receives will be fed into a logic system 62 comprising appropriately selected data processing and switching elements of known type. This system, acting in collaboration with a memory storage facility 63 to the extent indicated hereinafter, performs the functions of (a) directing motion of the motors M2 and M4 which successively engages the drive members 31 and 31a with the driving parts of the character-bearing structures a and 11a which are selected for such action by information appearing on the particular card being read, (b) directing motion of the motors M1 and M3 to drive to the respective printing stations 12 and 13 the characters designated for such action by the card being red, and (c) coacting with a monitoring system shortly to be described to compare systematically the successive attained positions of the drive members 31 and 31a (and the consequent positions of the character-bearing structures) with the positions dictated for these elements by the card-read input.

Let it be assumed that at the starting point of operation the driving members 31 and 31a are each located at a home base to which they have previously been guided by homing mechanisms, the nature of which will be described later. For example, the home base for member 31 might be the position in which it engages with the first of the drive wheels 20. Similarly, member 310 might be at home base while in engagement with the first of the drive wheels a. If the instructions introduced through the card reader 60 have dictated that character printing is to occur at the positions respectively represented by the first-in-line of the characterbearing structures 10a and 11a, no immediate axial motion of shafts and 31a will be called for, and motors M2 and M4 will temporarily remain unenergized.

Concurrently, the circuitry of the logic system will be addressing attention to control of the motor systems M1 and M3. Let it'tirst be assumed that, as a matter of chance, the first of the character-bearing structures 10a is in such position that the character borne by that structure which is called for by the card reader 60, acting through the logic is already at the printing station 12. Under these conditions, no energization of the motor system M1 will be called for as long as the driving member 31 remains in engagement with the first driving wheel 20. A similar rule applies, of course, in connection with the motor M3.

If, on the other hand, a printing'character other than that initially at the printing station is called for by the card reader input, this fact will be detected by the logic system 62, and motion of the appropriate motor system (M1 or M3) will be initiated by the logic system operating through conventional switching devices (not shown) which it incorporates or controls Focusing on the motor system M1, this system will, under the conditions just predicated, act through the gear combination 35, 36, the shaft 30, the drive member 31 and the wheel 20 to rotate the first belt 10a backward or forward until the desired printing character has reached the printing station 12. The motor system M3 works in similar fashrun.

We now consider the means by which, in accordance with our invention, positioning of a desired character at the printing station is accomplished in each case with high accuracy and reliability and with assurance that any error in positioning will be detected and signalled.

OUTPUT CONTROL AND MONITORING MEANS Close control of the positioning of the printing charments of the shafts and 500 which occur and to communicate their occurrence to the memory storage station 63. Here the number of successive movements which have occurred while any given one of the character-bearing structures is being driven by the associated motive system will be cumulated or counted by an appropriate memory register. Moreover, the count so made will be compared with a number derived, for example, directly or indirectly from the input from the card reader as representative of the total number of incremental movements required to bring the particular character to be printed into location at the associated printing station. When an exact matching of the cumulative count and the required number occurs, the logic system will recognize that the given character has in fact reached the printing station, and a circuit condition will automatically be established to terminate motion of the character-bearing structure concerned. This will, of course, be accomplished by temporary deenergization through well-known switching means of the motive system by which the motion is produced. The logic system will then be directed by the instructions introduced through the card reader 60 to intiate motion of drive member 31 or 310, as the case may be, toward engagement with the next succeeding character-bearing structure which is to be employed in the printing operation that is being set up.

This will be done by action of the logic system in applying power (i.e. through known switching means) to motive system M2 or M4, as may be indicated. Output shafts 52 and 52a, of the motive systems M2 and M4 have associated with them signal-generating and transmitting devices 80 and 80a respectively which correspond in essential respects to the devices 70 and 70a already described. Specifically, these devices supply counting pulses to the memory storage 63 which, when compared with instructional information provided 7 through the logic system 63, will detennine when the drive members 31 and 310 have fully engagedthe next character-bearing structures which they are intended to engage. When this point is in fact reached, the systems M2 and M4 will again be de-energized by the logic system as long as the character-bearing structures in question are being driven in their character-positioning mode.

THE MOTION-MONITORING SYSTEM The electromechanical elements of the motionsensing-and-communicating system of FIG. 1 are shown in greater detail in FIGS. 2, 3, 4, and 5, it being understood that the constructions of these FIGURES are duplicated in the similar systems 70a, a and 80 of FIG. 1. Referring first to FIG. 2, there is shown in edgewise perspective a code wheel 71 mounted (as in FIG. 1) on shaft 50, by which it is rotated. This, of course, assures that the code wheel will move in synchronism (and in step) with the shaft 50, and consequently in step with the shaft 30 and its driven member 31. Embracing the code wheel at its upperedge is a yoke 72 assumed to be held fixedly in place by appropriate supporting means (not shown). The left branch of the yoke as oriented in FIG. 2 supports and partially encloses in recesses provided for the purpose three light sources (e.g. microlamps), of which two, numbered 73a and 730, appear in dotted outline in FIG. 2. A more complete picture of the relative location of these light sources is provided in FIG. 3, which is a sectional view of the yoke taken on line 3-3 of FIG. 2. Here are shown not only the light sources 73a and 73c, but also the third source 73b, which is in lateral alignment with 730.

The right branch of the yoke 72 supports and partially encloses three photocells of which two, numbered 740 and 740, can be seen in FIG. 2. Each of these (including the third cell which is not viewable in FIG. 2) is located in precise alignment across the yoke gap 75 with the correspondingly lettered one of the lamps 73a, 73b and 73c. The several lamps have power-supplying connections indicated at 76, and the photocells have output connections as indicated at 77.

The individual light source and photocell combinations constitute sensing devices of a kind well-known in the art. More specifically, each light cell is designed to produce a signal output at its leads 77 when it is illuminated by the corresponding light source and to produce no output or significantly diminished output when it is cut off from such illumination.

The coaction between the sensing devices so constituted and the code wheel 71 may be shown by refer ence to FIG. 4, in which a side view ofa segment of the wheel is presented. At its periphery the wheel is provided with a series of slots 90 bounded by teeth 91. As appears at the locations designated 90a, every fifth slot is differentiated in shape from the intervening slots for a purpose to be described at a later point.

Assuming, as suggested earlier in the more general description of the invention, that the stepping motor Ml of FIG. 1 requires 200 discrete incremental steps of motion to rotate the shaft 50 once, we provide, for reasons to be explained, a total of 25 slots and 25 teeth around the periphery of the code wheel 71 (and similarly for the remaining code wheels). Also, the slots and teeth should be substantially of the same circumferential width, so that four steps of motion are required to move the circumference of the wheel a distance corresponding to the width of either 5 single slot or a single tooth.

Under these conditions, let it be assumed that in the code wheel's initial position (i.e. before it is driven from its home base"), the photocell 74a lies, as shown in FIG. 4, within the boundaries of one slot and the adjacent photocell 74b lies (as shown) within the boundaries of the next adjoining tooth. Photocell 74c lies in the same slot as cell 74a, this being shown for purposes of illustration as one of the deeper slots 90a. Under the arrangement previous described, the light sources which respectively correspond to these photocells will lie in exactly analogous positions. Accordingly, cells 74a and 740 will be energized and cell 74b de-energized. It needs to be recognized that the particular dwell position of the wheel 71 as represented in FIG. 4 is preferably not such as to locate the cells 74a and 740 (or their coacting light sources 73a and 73b) precisely at the center of the slot in which they appear or to locate the cell 74b precisely behind the center of the tooth by which it is concealed. The preferred condition is illustrated in FIG, 5 which shows the tooth 91 presented there as being divided into four equal areas, a, b, c and d. In the dwell position which is shown, the cell 74b lies behind the center of area c. Assuming counterclockwise rotation of the code wheel (with resultant motion of the tooth 90 to the left), the next dwell position of the wheel would put the cell 74b behind the center of the area d it being recalled that eight discrete and equal motions of the stepping motor are required to rotate the code wheel the width of a combined tooth and slot (i.e. 8/200ths of the circumference of the entire wheel) By similar reasoning, one more discrete motion of the stepping motor will position the photocell 74b opposite the center of the first of the four quadral areas of the slot which lies to the right of the tooth 91. Moreover, the cell will have four positions of dwell within the boundaries of that slot during transition of all of which it will be exposed to illumination from the light source 74b.

The net result of the arrangement just described is that during the occurrence of any four successive step motions of the code wheel 71, the cell 740 and the cell 74b will both reverse their conditions of illumination, going from dark to light or light to dark, as the case may be. With consequences to be explained at a later point, the cell 740, once it becomes dark will remain so for 36 motor pulses, thereafter becoming light again for four pulses. Upon any such reversal of lighting codition a signal change will occur at the output terminals 77 of each of these cells. These signal changes are, for the purposes of the present invention, communicated to the memory device 63 of FIG. 1 by being separately impressed on a multipath communication channel 100 which connects with the memory device through a sig nal converter C1. The converter serves to change the signals which it receives from the photo sensors 740, b and 0 into a form registrable in a counting register provided in the memory 63.

As has been previously indicated, the function of the sensing-and-communicating device (and of the related and similarly functioning devices 70a, 80 and 80a) is to provide highly precise and reliable monitoring of the operation of the mechanical parts of the character-positioning apparatus as energized by input directions received through the card reader 60 and the logic system 62. It does this by comparing, no less often than every four steps of actual incremental motion of the shaft 50 in a single direction, the algebraic total of the back and forth steps that have occurred in both directions with the number of" steps demanded by the input to the logic system 62. from the card reader 60.

The system is saved from the possibility of ambiguity arising from the four-step" limitation imposed in the preceding sentence by the fact established in earlier explanation that to replace any given character momentarily located at a printing station by the next succeeding character requires eight incremental rotary movements of the shaft 50, and that a similar set of eight incremental axial movements of the shaft is required to move one of the driving members from full engagement with a given character-bearing structure to engagement with the next succeeding structure. Accordingly, it may be assumed that no instruction received and transmitted by the logic system 62 from input source 60 will call for incremental shaft movements other than in numbers which are multiples of eight and thus, necessarily, multiples of four. (It will, of course, be understood that if design considerations make this desirable, a higher multiple of four than eight for example, 16 can be stipulated as the number ofincremental motions required to move a character or character-bearing structure from one significant position to the next significant position, and that such a change will not impair the operability of the monitoring system being described.)

The comparison of actually counted and inputdemanded incremental movements may take place either in the memory device or in the logic system by provision in either of them of a count comparator of known type, or it may occur in a separate computing facility (not shown) to which the logic system and memory connected. A particular (although not the only) standard of reference with which the cumulative output of the sensor 72 may be compared is the algebraic sum of the backward and forward impulses actually supplied by or through the logic system to the stepping motor Ml. If any discrepancy is detected between the last-mentioned figure and the algebraically cumulated number of discrete back and forth motions observed by the sensor 70, there will necessarily have occurred a slippage between the input and output of the drive system, which slippage represents an error in performance. Detection of such an error will be communicated to the logic system 62 from the memory device 63 (if the comparison has been made there) through a communication channel 105. Upon receipt of the error signal, the logic system will, in accordance with design, act to shut down the system and/or supply a warning sign (e.g. a red light viewable by the operator of the apparatus). At this point, either the apparatus can be restarted by reintroduction of the control card (which is assumed for this purpose initially to drive all operating components back to home base") or if the error signal is repetitive, a search for the cause of difficulty can be instituted.

it will be understood that sensing and communicating devices 700, 80 and 800 function in a way entirely analogous to that of device 70, their pulse outputs being directed through channels 101, 102 and 103 to counting registers in memory 63. A discrepancy detected through the output of any one of these channels will, of course, act to stop the apparatus and provide an error signal to the operator so that corrective action can be taken.

It is a significant feature of the monitoring system as so far described that it has a built-in redundancy or fail safe capability. Specifically, either the combination of the light source 73a and the photocell detector 74a, standing alone, or the combination of the light source 73b and the photocell detector 74b, standing alone, can perform the counting and communicating operations upon which the monitoring function depends. This is because eachof these combinations is, in the presence of the moving code wheel, a pulse generator which produces pulses corresponding in number to the number of four-step movements of the code wheel. Therefore, the output of either combination, taken alone, will enable comparison of the number of actual incremental motions of the code wheel with the number of motions of the shaft 50 called for by the input to the logic system. Accordingly, failure of a single light source or a single photocell will not destroy or impair the monitoring function.

A still further safeguard against failure of this function is provided by the combination of the light source 73c and the photocell 74c coacting with the specially enlarged or deepened slots shown in FIGS. 4. As previously explained, only one in five slots (or, if desired, only every ath slot) provided a is a number which evenly divides the total number of slots in the code wheel) has the indicated enlargement. Also, the light source 73c and the photocell 74 are exposed to one another (and consequently produce a positive output pulse or signal) only when they come into coincidence with the enlarged slots as in the situation shown in FIG. 4. Thus, the photocell output provides a means for counting the number of 40-unit movements of the wheel 71 which take place, (ie the number ofpassages of five slots plus five teeth which occur). These counting signals as they appear at the terminals of the photocell 74a are impressed on the communication channel and by appropriate circuitry in the memory 63 are compared with the 40-count cumulations of energizing signals received from the system input. Again, any discrepancy in the two counts develops an error signal which will shut down the apparatus or alert the operator or both. Thus, there is provided a counting of incremental movements of the drive shaft 30 (and of the shaft 31) which is independent of, but cyclically conformatory of the counting accomplished by the photocells 740 and 74b. By this means (superimposed on the two-fold monitoring capability previously described), the apparatus is given three levels of assurance against undetected malfunction or failure of individual sensing elements.

HOMING PROVlSlONS lt simplifies the programming of apparatus such as that being described if the positioning instructions to be supplied can always assume that the apparatus initially has its operating parts in a predetermined home position. For this reason, the apparatus of the invention is provided with means for moving all of the characterbearing structures or belts and the two drive members 31 and 31a to a fixed terminal position in response to appropriate input instructions. The system can readily be programmed to perform the homing" operation either in response to the insertion of a blank card in the card reader, or by the provision on each card inserted of an instruction column at either end of the card which causes the homing operation to occur.

In the case of the drive members 31 and 31a, home positioning is most easily accomplished by energizing the step motors M2 and M4 to drive continuously in a single direction until a cut-off or stop signal is received. The stop signal is in this case produced by microswitches and 120a (FIG. 1) actuable by carrying members 38 and 38a, respectively, when they have reached a point of travel to the left which locates the drive members 31 and 31a in engagement with the first of the drive wheels 20 and 20a. Actuation of the switches 120 and 1200 conveys a signal to the logic system 62, or otherwise acts on the M2 and M4 to disable them from producing further leftward motion of the members 28 and 38a although renewed motion to the right must obviously not be precluded. Simultaneously, the part of the memory system which maintains a count of the incremental axial movements of the shafts 30 and 30a is brought back to what amounts to its zero position. Microswitches corresponding to switches 120 and 120a, although not shown, may also be positioned to be actuated when the carriers 38 and 38a reach their extreme righthand positions. Such microswitches serve first as a safety precaution against attempted over-travel to the right of the shafts 30 and 30a, and, secondly, provide capability of having a sec nd or righthand home position of the shafts if it is desired to do this for purposes of greater flexibility.

In respect to the character-bearing structures (e.g. belts) a and 110, a different kind of home signalling device is provided. This is illustrated in FIG. 6 where there is shown on enlarged scale a portion of one of the belts 10a in contact with the corresponding driving wheel 20. The belt is shown somewhat schematically as being segmented into discrete elements, three of which are respectively numbered 10a1, 10a2, and 10a3. Each of these segments other than 10a1 is to be understood as bearing on its outer surface a single alphanumeric or other printable character. The belt is considered to be in its home location when segment 10a1 lies in a critical position along its line of possible travel, this being, for example, the position illustrated in FIG. 6. In distinction from the other belt segments, segment 10a1 bears on or imbeddcd in its surface a raised planar reflective clement (e.g. a polished metal piece) 131.

Coacting with the reflector 131 is an optical sensing system I30 which utilizes collimated light beam 132 produced, for example, by the combination of a concentrated light source 133 anda collimating tube or lens 134. With the reflector 131 in the position in which it is shown, and only when it is in that position, the light beam 131 is able to travel by reflection from the element 131 through a small-dimensioned and strategically positioned aperture (or alternatively a tube) 136 into illuminating contact with a photocell or other light sensor 138. Upon impingement of the light beam on the sensor, there is generated at the output terminals 140 of the sensor a pulse or signal declarative of the arrival of the segment 10a1, and consequently of the belt 100 as a whole, at its home position. Moreover, with the high-accuracy optical system described, this signal can only occur when the segment 10a] is very precisely located at the prescribed position. Any position of the segment either to the right or left of the prescribed position will produce inclination of the reflector 131 and necessarily prevent the reflected beam 132 from reaching the sensor 138.

The home-indicating signal generated at the terminals 140 when the belt segment 10a1 is in its prescribed position is communicated through an appropriate electrical channel 145 (FIG. 1) to the logic system 62 and acts through that system immediately to discontinue further home-seeking motion of the belt 10a. This it does, of course, by temporarily de-energizing the motor M2 of FIG. 1.

Each ofthe belts 10a and 11a is controlled in its homing function in the manner just described. While each individual belt could be provided with a complete optical system of the type illustrated in FIG. 6, unnecessary duplication of parts is achieved as illustrated in FIG. 1 by mounting each of the optical assemblies 130 and 130a on a frame which is moved axially in unison with its associated shaft (i.e. 30 or 30a) and is aligned so that it coacts with the reflective area on each belt in turn.

GEAR-ENGAGING PROVISIONS It is, of course, important that the driving gear members 31 and 31a engage readily and without possibility of blockage or excessive friction when they move from contact with one of the driven members 32 and 32a to the next or a succeeding one of these latter members. This is accomplished in the present apparatus by permitting a certain amount of backlash between these gears parts, and by controlling the rotary motion of the gear members 31 and 31a in such a way as to take advantageof this condition. Specifically, the control program of the logic system is adjusted to effect a single back-off step of the driving member either as it comes to rest or, in any event, before movement from one engaging position to the next.

The significance of this is illustrated in FIGS. 7 and 7a, considered jointly. In FIG. 7 the driving gear 31 is shown in the position in respect to the driven gear surface 32 which it will occupy during and at the end of a driving cycle, assuming clockwise rotation of the gear 31. The primary driving tooth of the gear 31 is shown in face-to-face engagement at surface a with the primary driven tooth of the gear 32. Because of the precision with which the entire gearing apparatus is built, the various belt-driving gears which lie behind the particular gear 32 selected for illustration, having each been disengaged at the end of a driving cycle, will be in substantially identical positions to that of the illustrated gear, subject only to tolerance-permitted variations. Nevertheless, the latter variations may be great enough to cause at least frictional resistance to initial entry of the gear 31 into driving engagement with some or all of the succeeding gears. To minimize operating difficulties attributable to this cause, we include in the control function of the logic system 62 (FIG. 1), the condition that the gear 31 shall be rotated one discrete step (i.e. l/200th of a revolution) backward before it initiates movement toward engagement with a new one of the succession of driven gears 32. The designed backlash or clearance between the teeth of the gears 31 and 32 is such that this degree of movement brings the primary tooth (as heretofore identified) of the gear 31 into the relative position respecting the adjacent teeth of the gear 32 which is shown in FIG. 7a. That is to say, about 1 degree of clearance freedom is introduced at b (FIG. 7a) between the faces of the two gears which are opposed at that location. Moreover, the backlash allowance of the gear system is such that similar clearance exists at the other side of the active gear tooth as indicated at c. Under these conditions, entry of the gear 31 into the inter-teethspaces of any of the gears 32 which it required to traverse or engage will be substan tially frictionless.

The unitary backward motion of the gear 31 which is specified in the immediately preceding description introduces a temporary error or aberration of one in the eight-pulse counting system on vhich control and monitoring of the belt drive system is based. However, this error is reversed and in effect erased by the circumstance that, upon return to its driving mode, the gear 31 (and the associated shaft 30) will require nine impulses in the driving direction to accomplish one full character displacement of the particular characterbearing structure which is being newly engaged. The first of these impulses will simply restore the gear 31 and the shaft 30 to the positions which they occupied before the single pulse back-off motion was introduced. Concurrently, the code wheel 71, which moves synchronously with the shaft 30 will also be restored to its former position. Accordingly, when active driving engagement begins, following the first of nine driving pulses, only the remaining eight pulses (of the group of nine) will be required to drive all parts to the next normal dwell points they would all have occupied after eight driving pulses had the friction-reducing backward motion never been introduced. This represents, therefore, a return to counting normalcy.

It will thus be seen that the objects set forth above, among those made apparent from the preceding description, are efficiently attained and, since certain changes may be made in the above constructions without departing from the scope of the invention, it is intended that all matter contained in the above description or shown in the accompanying drawings shall be interpreted as illustrative and not in a limiting sense.

Having described our invention, what we claim as new and desire to secure by Letters Patent is:

l. Print-setting apparatus comprising, in combination:

A. printing means having a plurality of separate but similar character-bearing structurSs in a common assembly, each structure being movable independently of the other for successively positioning the various characters carried by it in a printproducing location;

B. a first drive means including a drive shaft mounting a drive member for selective engagement with the several character-bearing structures, said drive shaft being rotatable to move the drive member engaged structure in discrete incremental steps of various possible positions;

C. a second drive means for selectively moving the drive member into engagement with any one of the several character-bearing structures;

D. means for energizing said first and second drive means for incremental movement; and

Ev means for determining the ultimate position to which each character-bearing structure will be driven, said means comprising l. first and second sensing means respectively operatively associated with the first and second drive means for sensing incremental movements of the respective drive means,

2. the first sensing means including a. a code wheel driven synchronously with said drive shaft and having a number of alternated teeth and slots of substantially identical circumferential extent, every ath slot of the code wheel is distinctively shaped, a being a number which evenly divides the total number of slots on the code wheel, and

b. a sensor including a first light source and photocell combination positioned to provide a signal pulse upon passage by it of every transition between a slot and a tooth of the code wheel, the number of incremental steps required for a single rotation of the drive shaft being in exact multiple of the number signal pulses produced by the first light source and photocell combination during a signal rotation of the code wheel, whereby counting said signal pulses provides a precise indication ofthe achieved degree of rotation of the drive shaft, and a second light source and photocell combination positioned to provide a signal pulse only upon passage by it of a transition between one of said distinctively shaped siots and an enjoining tooth, whereby said last-mentioned signal pulses product a counting of incremental movements of the drive shaft which is independent of but cyclically confirmatory the counting of such movements provided by signal pulses produced by the first light source and photocell combination, and 3. a logic system connected with the sensing means for counting the signal pulses and terminating movement of said first drive means when the numbers of accumulated pulses meet criteria pre-established in the logic system.

2. Print-setting apparatus comprising in combination:

A. printing means having a plurality of separate but similar character-bearing structures in side-by-side relationship, each structure being movable independently of the others for successively positioning the various characters carried by it in a printproducing location,

B. a first drive means having a drive member selec tively engageable with the several characterbearing structures and operable when engaged with a particular structure to move the engaged structure into its various possible positions,

C. a second drive means for selectively driving the drive member into engagement with any one of the several character-bearing structures,

D. means for energizing the second drive means for engaging movement,

E. electrical power means for energizing the first drive means for character-positioning movement of the engaged character-bearing structure in discrete incremental steps,

F. counting means associated with the said first drive means for counting the number of incremental steps imparted to the engaged character-bearing structure, and

G. means for automatically terminating motion of the character-bearing structure when the counting means signals arrival at the print-producing location ofa desired one of the characters borne by the structure, said means including further means for .producing a single backward incremental step of the drive member to facilitate engagement of the drive member with the next character-bearing structure which it is driven to engage.

3. Print-setting apparatus according to claim 2 in which A. each character-bearing structure has associated with it means for signalling arrival of the structure at a home base location which it is desired that it occupy at the time of initiation of operation of the apparatus, such means comprising 1. an optically reflecting device carried by character-bearing structures,

2. light-producing means adapted to reflect light from each of the reflecting devices when it reaches a predetermined position indicative of the arrival of the associated character-bearing structure at approximately its designated home base location, and

3. means responsive to a critically oriented reflection of light from a reflecting device for causing cessation of movement of the associated character-bearing structure when it has arrived precisely at its desired home base position.

* i l i 

1. Print-setting apparatus comprising, in combination: A. printing means having a plurality of separate but similar character-bearing structures in a common assembly, each structure being movable independently of the other for successively positioning the various Characters carried by it in a print-producing location; B. a first drive means including a drive shaft mounting a drive member for selective engagement with the several characterbearing structures, said drive shaft being rotatable to move the drive member engaged structure in discrete incremental steps to various possible positions; C. a second drive means for selectively moving the drive member into engagement with any one of the several character-bearing structures; D. means for energizing said first and second drive means for incremental movement; and E. means for determining the ultimate position to which each character-bearing structure will be driven, said means comprising
 1. first and second sensing means respectively operatively associated with the first and second drive means for sensing incremental movements of the respective drive means,
 2. the first sensing means including a. a code wheel driven synchronously with said drive shaft and having a number of alternated teeth and slots of substantially identical circumferential extent, every ath slot of the code wheel is distinctively shaped, a being a number which evenly divides the total number of slots on the code wheel, and b. a sensor including a first light source and photocell combination positioned to provide a signal pulse upon passage by it of every transition between a slot and a tooth of the code wheel, the number of incremental steps required for a single rotation of the drive shaft being in exact multiple of the number signal pulses produced by the first light source and photocell combination during a single rotation of the code wheel, whereby counting said signal pulses provides a precise indication of the achieved degree of rotation of the drive shaft, and a second light source and photocell combination positioned to provide a signal pulse only upon passage by it of a transition between one of said distinctively shaped slots and an enjoining tooth, whereby said last-mentioned signal pulses product a counting of incremental movements of the drive shaft which is independent of but cyclically confirmatory the counting of such movements provided by signal pulses produced by the first light source and photocell combination, and
 3. a logic system connected with the sensing means for counting the signal pulses and terminating movement of said first drive means when the numbers of accumulated pulses meet criteria pre-established in the logic system.
 2. the first sensing means including a. a code wheel driven synchronously with said drive shaft and having a number of alternated teeth and slots of substantially identical circumferential extent, every ath slot of the code wheel is distinctively shaped, a being a number which evenly divides the total number of slots on the code wheel, and b. a sensor including a first light source and photocell combination positioned to provide a signal pulse upon passage by it of every transition between a slot and a tooth of the code wheel, the number of incremental steps required for a single rotation of the drive shaft being in exact multiple of the number signal pulses produced by the first light source and photocell combination during a single rotation of the code wheel, whereby counting said signal pulses provides a precise indication of the achieved degree of rotation of the drive shaft, and a second light source and photocell combination positioned to provide a signal pulse only upon passage by it of a transition between one of said distinctively shaped slots and an enjoining tooth, whereby said last-mentioned signal pulses product a counting of incremental movements of the drive shaft which is independent of but cyclically confirmatory the counting of such movements provided by signal pulses produced by the first light source and photocell combination, and
 2. light-producing means adapted to reflect light from each of the reflecting devices when it reaches a predetermined position indicative of the arrival of the associated character-bearing structure at approximately its designated home base location, and
 2. Print-setting apparatus comprising in combination: A. printing means having a plurality of separate but similar character-bearing structures in side-by-side relationship, each structure being movable independently of the others for successively positioning the various characters carried by it in a print-producing location, B. a first drive means having a drive member selectively engageable with the several character-bearing structures and operable when engaged with a particular structure to move the engaged structure into its various possible positions, C. a second drive means for selectively driving the drive member into engagement with any one of the several character-bearing structures, D. means for energizing the second drive means for engaging movement, E. electrical power means for energizing the first drive means for character-positioning movement of the engaged character-bearing structure in discrete incremental steps, F. counting means associated with the said first drive means for counting the number of incremental steps imparted to the engaged character-bearing structure, and G. means for automatically terminating motion of the character-bearing structure when the counting means signals arrival at the print-producing location of a desired one of the characters borne by the structure, said means including further means for producing a single backward incremental step of the drive member to facilitate engagement of the dRive member with the next character-bearing structure which it is driven to engage.
 3. Print-setting apparatus according to claim 2 in which A. each character-bearing structure has associated with it means for signalling arrival of the structure at a home base location which it is desired that it occupy at the time of initiation of operation of the apparatus, such means comprising
 3. a logic system connected with the sensing means for counting the signal pulses and terminating movement of said first drive means when the numbers of accumulated pulses meet criteria pre-established in the logic system.
 3. means responsive to a critically oriented reflection of light from a reflecting device for causing cessation of movement of the associated character-bearing structure when it has arrived precisely at its desired home base position. 